The Dutchman joined the Premier League club from AZ for around £17 million in the summer of 2016.
But he struggled to settle in England and has scored just two goals in 31 top-flight appearances.
Dutch outlet VI reports that the 25-year-old is set to join Monterrey this week in a deal worth around €7m (£6.3m).
Janssen was loaned to Fenerbahce for the 2017/18 season but struggled with injury, before returning to north London last term and making just three substitute appearances.
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